1. Field of the Invention
The invention relates to an additive combination of a polymeric substance featuring poly (isomerized C.sub.12 -C.sub.50 monoolefin) structure with a lubricating oil pour depressant having alkyl side chains of 6 to 32 carbon atoms as middle distillate fuel flow improvers.
2. Description of the Prior Art
Kerosene, which is a solvent for wax, has traditionally been a component of middle distillate fuel oils, e.g. diesel fuels, home heating oils, etc. With the demands for kerosene for use in jet fuels, the amount of kerosene used in distillate fuel oils have decreased over the years. This, in turn, has frequently required the addition of wax crystal modifiers, e.g. pour point depressant additives, to the fuel oil to make up the lack of kerosene. Included therein are lubricating oil pour point depressant additives, namely, alkylated aromatics, particularly wax-naphthalene, for middle distillate fuels (J.S. Pat. No. 3,245,766).
Other fuel oil pour depressants include: polymerization products of a mixture of normal C.sub.10 -C.sub.26 alpha-olefins, said polymerization being carried out in the presence of a Friedel-Crafts catalyst as aluminum chloride (U.S. Pat. No. 3,252,771); and, copolymers of monoolefin mixtures, at least one of said monoolefins having an unbranched saturated hydrocarbon chain of at least 18 carbon atoms (British Pat. Spec. No. 1,154,966).
Other publications teach improving the cold flow properties of middle distillate fuels with various combinations, including: the combination of C.sub.24 -C.sub.50 carbon content .alpha.-olefins, ethylene-vinyl acetate copolymers and beeswax (U.S. Pat. No. 4,019,878); the combination of an N-aliphatic hydrocarbyl carbyl succinamic acid or its derivative with a poly (.alpha.-olefin), with an .alpha.-olefin or with an alkylated aromatic compound, i.e. alkylated diphenyl (U.S. Pat. No. 4,014,663); and the combination of ethylene-vinyl acetate copolymer and copolymers of ethylene with C.sub.2 -C.sub.18 .alpha.-olefins (U.S. Pat. No. 3,639,226).